Pomona College, Clareniont, California 145 



8. As a rule the size of the animal makes for a more complex 

 nervous system. Large animals have more and larger cells than 

 related small ones. In the same species embryonic nerve cells may 

 be much smaller than those of the adult, and the proportionate 

 number of cells is greater in certain embryonic stages. 



9. Vertebrates and invertebrates are similar as to function of 

 the central nervous system, but the centers are as different as are 

 the peripheral parts. 



10. The resemblances which ha\e been found in certain arachnid 

 and arachnid-like forms to the structures of vertebrate brains, it 

 seems to me, are but chance resemblances, analogous, but not 

 homologus, structures. In certain annelids the olfactory portion of 

 the brain is enormously developed for a special adaptation in a 

 limited group of worms. This great olfactory area might be com- 

 pared to the olfactory portion of the fore-brain of vertebrates, but 

 I think it is clear that we have an analogy merely. 



The comparisons of the nervous systems of nemertine worms 

 with those of vertebrates are interesting, but not necessarily sig- 

 nificant of relationships. 



The segmental character of the radial ner\"0us system of brittle 

 stars might be taken as an indication of relationship to segmented 

 animals with about as much justification. 



11. The degree of development of intelligence and instinct, I 

 believe, may be judged to some degree by the relative size of those 

 parts of the brain which are not directly or intimately connected 

 with the sense organs, such as the posterior region of the brain in 

 many segmental animals, or the region of the mushroom bodies of 

 some arthropods and others. 



12. If there is any higher psycical center in invertebrates, it 

 seems to me that it must be in the region not dominated by any one 

 center or sense and receiving fibers from all, a center well supplied 

 with nerve cells. Such a center may be the posterior portion of the 

 brain in certain segmented animals. 



13. The functional divisions are not well known. In those 

 forms where I have traced the motor and sensory fibers they were 

 mingled in the same nerve trunks in lower regions. The suggestions 

 of some that sensory areas in insects' ventral ganglia are ventral. 



